The proposed resource will generate, a complete microarray dissection of gene expression in the mouse immune system, focused on primary cells ex vivo, in basal conditions or in response to genetic or environmental perturbations. A group of immunology experts will prepare, under standardized conditions, RNA from 175 populations of the innate and adaptive immune systems. These will include all lymphoid cell types, their precursors, and their variants in lymphoid organs and in different tissues, as well as the main myeloid lineages (DC, macrophages, neutrophils) and immunologically relevant stroma. Genome-wide expression profiles will be obtained from these RNAs by high-throughput microarray technology. In addition, we will generate expression profiles for T and B lymphocytes, Treg and NK cells from a panel of 48 inbred mouse strains, and segregating intercross animals (F2 and Heterogeneous Stock mice), providing a unique perspective on genomic variability in the Mus species. We will use these data to define the connectivity between genes and the regulatory interactions that occur in the operation of the immune system, using sophisticated computational tools that have proven very powerful in microbial systems; we will identify "gene signatures" that characterize lymphoid lineages and the progression through differentiation steps. The computational predictions will then be tested/validated by modulating the expression of key genes by RNA interference, using lentiviral vectors to introduce RNAi effectors into mouse stem cells or embryos.The compendium of expression profiles, strain variability and the description of genomic networks and signatures will be made publicly accessible via electronic means, with rapid data release on the ImmGen site. In addition, we will develop, evaluate and deploy novel interactive methods for visual analysis, using sophisticated graphic vocabulaires from the scientific visualization field. This resource should prove very useful to support investigations of the normal and pathological immune system.We will use high-throughput genomic, bioinformatic and computer graphic technologies to determine, uniformly and reliably, the complete profiles and regulation of gene activity in the immune system. This will form an essential foundation for the exploration of immune and autoimmune diseases.